llkd: Add stack symbol checking

Feature outlined here is only available on userdebug or eng builds.
Blocked for security reasons because requires ptrace capabilities.

Add ro.llk.stack to list a set of symbols that should rarely happen
but if persistent in multiple checks, indicates a live lock condition.
At ro.llk.stack.timeout_ms the process is sent a kill, if it remains,
then panic the kernel.

There is no ABA detection in the paths, the condition for the
stack symbol being present instantaneously must be its rarity of
being caught.  If a livelock occurs in the path of the symbol, then
it is possible more than one path could be stuck in the state, but
the best candidate symbols are found underneath a lock resulting in
only one process being the culprit, and the best aim.  There may be
processes that induce a look of persistence, if so the symbol is not
a candidate for checking.

Add ro.llk.blacklist.process.stack to list process names we want
to skip checking.  This configuration parameter is also used to
prevent sepolicy noise when trying to acquire stacks from non
ptrace'able services.

Test: gTest llkd_unit_tests
Bug: 33808187
Bug: 111910505
Bug: 80502612
Change-Id: Ie71221e371b189bbdda2a1155d47826997842dcc

7 files changed, 278 insertions, 33 deletions

diff --git a/llkd/Android.bp b/llkd/Android.bp
index a6edd26ce..62a637dcd 100644
--- a/llkd/Android.bp
+++ b/llkd/Android.bp
@@ -20,6 +20,12 @@ cc_library_static {
     export_include_dirs: ["include"],
 
     cflags: ["-Werror"],
+
+    product_variables: {
+        debuggable: {
+            cppflags: ["-D__PTRACE_ENABLED__"],
+        },
+    },
 }
 
 cc_binary {
@@ -39,4 +45,9 @@ cc_binary {
     cflags: ["-Werror"],
 
     init_rc: ["llkd.rc"],
+    product_variables: {
+        debuggable: {
+            init_rc: ["llkd-debuggable.rc"],
+	},
+    },
 }
diff --git a/llkd/README.md b/llkd/README.md
index 231458365..1f69718a1 100644
--- a/llkd/README.md
+++ b/llkd/README.md
@@ -23,6 +23,9 @@ the period of time before the next expected call to this handler.
 Operations
 ----------
 
+There are two detection scenarios. Persistent D or Z state, and persistent
+stack signature.
+
 If a thread is in D or Z state with no forward progress for longer than
 ro.llk.timeout_ms, or ro.llk.[D|Z].timeout_ms, kill the process or parent
 process respectively.  If another scan shows the same process continues to
@@ -32,6 +35,26 @@ condition.  Add a alarm self watchdog should llkd ever get locked up that is
 double the expected time to flow through the mainloop.  Sampling is every
 ro.llk_sample_ms.
 
+For usedebug releases only, persistent stack signature checking is enabled.
+If a thread in any state but Z, has a persistent listed ro.llk.stack kernel
+symbol always being reported, even if there is forward scheduling progress, for
+longer than ro.llk.timeout_ms, or ro.llk.stack.timeout_ms, then issue a kill
+to the process.  If another scan shows the same process continues to exist,
+then have a confirmed live-lock condition and need to panic.  There is no
+ABA detection since forward scheduling progress is allowed, thus the condition
+for the symbols are:
+
+- Check is looking for " " + __symbol__+ "0x" in /proc/<pid>/stack.
+- The __symbol__ should be rare and short lived enough that on a typical
+  system the function is seen at most only once in a sample over the timeout
+  period of ro.llk.stack.timeout_ms, samples occur every ro.llk.check_ms. This
+  can be the only way to prevent a false trigger as there is no ABA protection.
+- Persistent continuously when the live lock condition exists.
+- Should be just below the function that is calling the lock that could
+  contend, because if the lock is below or in the symbol function, the
+  symbol will show in all affected processes, not just the one that
+  caused the lockup.
+
 Default will not monitor init, or [kthreadd] and all that [kthreadd] spawns.
 This reduces the effectiveness of llkd by limiting its coverage.  If there is
 value in covering [kthreadd] spawned threads, the requirement will be that
@@ -40,7 +63,9 @@ to recover the thread should it be killed externally (this is good driver
 coding hygiene, a common request to add such to publicly reviewed kernel.org
 maintained drivers).  For instance use wait_event_interruptible() instead of
 wait_event().  The blacklists can be adjusted accordingly if these
-conditions are met to cover kernel components.
+conditions are met to cover kernel components.  For the stack symbol checking,
+there is an additional process blacklist so that we do not incide sepolicy
+violations on services that block ptrace operations.
 
 An accompanying gTest set have been added, and will setup a persistent D or Z
 process, with and without forward progress, but not in a live-lock state
@@ -93,14 +118,31 @@ default ro.llk.timeout_ms, D maximum timelimit.
 #### ro.llk.Z.timeout_ms
 default ro.llk.timeout_ms, Z maximum timelimit.
 
+#### ro.llk.stack.timeout_ms
+default ro.llk.timeout_ms,
+checking for persistent stack symbols maximum timelimit.
+Only active on userdebug and eng builds.
+
 #### ro.llk.check_ms
 default 2 minutes samples of threads for D or Z.
 
+#### ro.llk.stack
+default *empty* or false, comma separated list of kernel symbols.
+The string "*false*" is the equivalent to an *empty* list.
+Look for kernel stack symbols that if ever persistently present can
+indicate a subsystem is locked up.
+Beware, check does not on purpose do forward scheduling ABA except by polling
+every ro.llk_check_ms over the period ro.llk.stack.timeout_ms, so stack symbol
+should be exceptionally rare and fleeting.
+One must be convinced that it is virtually *impossible* for symbol to show up
+persistently in all samples of the stack.
+Only active on userdebug and eng builds.
+
 #### ro.llk.blacklist.process
 default 0,1,2 (kernel, init and [kthreadd]) plus process names
 init,[kthreadd],[khungtaskd],lmkd,lmkd.llkd,llkd,watchdogd,
 [watchdogd],[watchdogd/0],...,[watchdogd/***get_nprocs**-1*].
-The string false is the equivalent to an empty list.
+The string "*false*" is the equivalent to an *empty* list.
 Do not watch these processes.  A process can be comm, cmdline or pid reference.
 NB: automated default here can be larger than the current maximum property
 size of 92.
@@ -108,15 +150,23 @@ NB: false is a very very very unlikely process to want to blacklist.
 
 #### ro.llk.blacklist.parent
 default 0,2 (kernel and [kthreadd]).
-The string false is the equivalent to an empty list.
+The string "*false*" is the equivalent to an *empty* list.
 Do not watch processes that have this parent.
 A parent process can be comm, cmdline or pid reference.
 
 #### ro.llk.blacklist.uid
 default *empty* or false, comma separated list of uid numbers or names.
-The string false is the equivalent to an empty list.
+The string "*false*" is the equivalent to an *empty* list.
 Do not watch processes that match this uid.
 
+#### ro.llk.blacklist.process.stack
+default process names init,lmkd,lmkd.llkd,llkd,keystore,logd.
+The string "*false*" is the equivalent to an *empty* list.
+This subset of processes are not monitored for live lock stack signatures.
+Also prevents the sepolicy violation associated with processes that block
+ptrace, as these can not be checked anyways.
+Only active on userdebug and eng builds.
+
 Architectural Concerns
 ----------------------
 
diff --git a/llkd/include/llkd.h b/llkd/include/llkd.h
index e3ae4bbd8..d0188ec79 100644
--- a/llkd/include/llkd.h
+++ b/llkd/include/llkd.h
@@ -43,9 +43,12 @@ unsigned llkCheckMilliseconds(void);
 #define KHT_TIMEOUT_PROPERTY           "ro.khungtask.timeout"
 #define LLK_D_TIMEOUT_MS_PROPERTY      "ro.llk.D.timeout_ms"
 #define LLK_Z_TIMEOUT_MS_PROPERTY      "ro.llk.Z.timeout_ms"
+#define LLK_STACK_TIMEOUT_MS_PROPERTY  "ro.llk.stack.timeout_ms"
 #define LLK_CHECK_MS_PROPERTY          "ro.llk.check_ms"
 /* LLK_CHECK_MS_DEFAULT = actual timeout_ms / LLK_CHECKS_PER_TIMEOUT_DEFAULT */
 #define LLK_CHECKS_PER_TIMEOUT_DEFAULT 5
+#define LLK_CHECK_STACK_PROPERTY       "ro.llk.stack"
+#define LLK_CHECK_STACK_DEFAULT        ""
 #define LLK_BLACKLIST_PROCESS_PROPERTY "ro.llk.blacklist.process"
 #define LLK_BLACKLIST_PROCESS_DEFAULT  \
     "0,1,2,init,[kthreadd],[khungtaskd],lmkd,lmkd.llkd,llkd,watchdogd,[watchdogd],[watchdogd/0]"
@@ -53,6 +56,8 @@ unsigned llkCheckMilliseconds(void);
 #define LLK_BLACKLIST_PARENT_DEFAULT   "0,2,[kthreadd]"
 #define LLK_BLACKLIST_UID_PROPERTY     "ro.llk.blacklist.uid"
 #define LLK_BLACKLIST_UID_DEFAULT      ""
+#define LLK_BLACKLIST_STACK_PROPERTY   "ro.llk.blacklist.process.stack"
+#define LLK_BLACKLIST_STACK_DEFAULT    "init,lmkd.llkd,llkd,keystore,/system/bin/keystore"
 /* clang-format on */
 
 __END_DECLS
diff --git a/llkd/libllkd.cpp b/llkd/libllkd.cpp
index bb55d1fee..58c2ba8d2 100644
--- a/llkd/libllkd.cpp
+++ b/llkd/libllkd.cpp
@@ -73,7 +73,14 @@ bool llkRunning = false;                             // thread is running
 bool llkMlockall = LLK_MLOCKALL_DEFAULT;             // run mlocked
 bool llkTestWithKill = LLK_KILLTEST_DEFAULT;         // issue test kills
 milliseconds llkTimeoutMs = LLK_TIMEOUT_MS_DEFAULT;  // default timeout
-enum { llkStateD, llkStateZ, llkNumStates };         // state indexes
+enum {                                               // enum of state indexes
+    llkStateD,                                       // Persistent 'D' state
+    llkStateZ,                                       // Persistent 'Z' state
+#ifdef __PTRACE_ENABLED__                            // Extra privileged states
+    llkStateStack,                                   // stack signature
+#endif                                               // End of extra privilege
+    llkNumStates,                                    // Maxumum number of states
+};                                                   // state indexes
 milliseconds llkStateTimeoutMs[llkNumStates];        // timeout override for each detection state
 milliseconds llkCheckMs;                             // checking interval to inspect any
                                                      // persistent live-locked states
@@ -83,6 +90,10 @@ bool khtEnable = LLK_ENABLE_DEFAULT;                 // [khungtaskd] panic
 // Provides a wide angle of margin b/c khtTimeout is also its granularity.
 seconds khtTimeout = duration_cast<seconds>(llkTimeoutMs * (1 + LLK_CHECKS_PER_TIMEOUT_DEFAULT) /
                                             LLK_CHECKS_PER_TIMEOUT_DEFAULT);
+#ifdef __PTRACE_ENABLED__
+// list of stack symbols to search for persistence.
+std::unordered_set<std::string> llkCheckStackSymbols;
+#endif
 
 // Blacklist variables, initialized with comma separated lists of high false
 // positive and/or dangerous references, e.g. without self restart, for pid,
@@ -97,6 +108,11 @@ std::unordered_set<std::string> llkBlacklistProcess;
 std::unordered_set<std::string> llkBlacklistParent;
 // list of uids, and uid names, to skip, default nothing
 std::unordered_set<std::string> llkBlacklistUid;
+#ifdef __PTRACE_ENABLED__
+// list of names to skip stack checking. "init", "lmkd", "llkd", "keystore" or
+// "logd" (if not userdebug).
+std::unordered_set<std::string> llkBlacklistStack;
+#endif
 
 class dir {
   public:
@@ -263,6 +279,9 @@ struct proc {
                                    // forward scheduling progress.
     milliseconds update;           // llkUpdate millisecond signature of last.
     milliseconds count;            // duration in state.
+#ifdef __PTRACE_ENABLED__          // Privileged state checking
+    milliseconds count_stack;      // duration where stack is stagnant.
+#endif                             // End privilege
     pid_t pid;                     // /proc/<pid> before iterating through
                                    // /proc/<pid>/task/<tid> for threads.
     pid_t ppid;                    // /proc/<tid>/stat field 4 parent pid.
@@ -272,6 +291,9 @@ struct proc {
     std::string cmdline;           // cached /cmdline content
     char state;                    // /proc/<tid>/stat field 3: Z or D
                                    // (others we do not monitor: S, R, T or ?)
+#ifdef __PTRACE_ENABLED__          // Privileged state checking
+    char stack;                    // index in llkCheckStackSymbols for matches
+#endif                             // and with maximum index PROP_VALUE_MAX/2.
     char comm[TASK_COMM_LEN + 3];  // space for adding '[' and ']'
     bool exeMissingValid;          // exeMissing has been cached
     bool cmdlineValid;             // cmdline has been cached
@@ -286,11 +308,17 @@ struct proc {
           nrSwitches(0),
           update(llkUpdate),
           count(0ms),
+#ifdef __PTRACE_ENABLED__
+          count_stack(0ms),
+#endif
           pid(pid),
           ppid(ppid),
           uid(-1),
           time(time),
           state(state),
+#ifdef __PTRACE_ENABLED__
+          stack(-1),
+#endif
           exeMissingValid(false),
           cmdlineValid(false),
           updated(true),
@@ -343,6 +371,10 @@ struct proc {
     void reset(void) {  // reset cache, if we detected pid rollover
         uid = -1;
         state = '?';
+#ifdef __PTRACE_ENABLED__
+        count_stack = 0ms;
+        stack = -1;
+#endif
         cmdline = "";
         comm[0] = '\0';
         exeMissingValid = false;
@@ -667,6 +699,48 @@ long long getSchedValue(const std::string& schedString, const char* key) {
     return ret;
 }
 
+#ifdef __PTRACE_ENABLED__
+bool llkCheckStack(proc* procp, const std::string& piddir) {
+    if (llkCheckStackSymbols.empty()) return false;
+    if (procp->state == 'Z') {  // No brains for Zombies
+        procp->stack = -1;
+        procp->count_stack = 0ms;
+        return false;
+    }
+
+    // Don't check process that are known to block ptrace, save sepolicy noise.
+    if (llkSkipName(std::to_string(procp->pid), llkBlacklistStack)) return false;
+    if (llkSkipName(procp->getComm(), llkBlacklistStack)) return false;
+    if (llkSkipName(procp->getCmdline(), llkBlacklistStack)) return false;
+
+    auto kernel_stack = ReadFile(piddir + "/stack");
+    if (kernel_stack.empty()) {
+        LOG(INFO) << piddir << "/stack empty comm=" << procp->getComm()
+                  << " cmdline=" << procp->getCmdline();
+        return false;
+    }
+    // A scheduling incident that should not reset count_stack
+    if (kernel_stack.find(" cpu_worker_pools+0x") != std::string::npos) return false;
+    char idx = -1;
+    char match = -1;
+    for (const auto& stack : llkCheckStackSymbols) {
+        if (++idx < 0) break;
+        if (kernel_stack.find(" "s + stack + "+0x") != std::string::npos) {
+            match = idx;
+            break;
+        }
+    }
+    if (procp->stack != match) {
+        procp->stack = match;
+        procp->count_stack = 0ms;
+        return false;
+    }
+    if (match == char(-1)) return false;
+    procp->count_stack += llkCycle;
+    return procp->count_stack >= llkStateTimeoutMs[llkStateStack];
+}
+#endif
+
 // Primary ABA mitigation watching last time schedule activity happened
 void llkCheckSchedUpdate(proc* procp, const std::string& piddir) {
     // Audit finds /proc/<tid>/sched is just over 1K, and
@@ -731,7 +805,15 @@ void llkLogConfig(void) {
               << LLK_TIMEOUT_MS_PROPERTY "=" << llkFormat(llkTimeoutMs) << "\n"
               << LLK_D_TIMEOUT_MS_PROPERTY "=" << llkFormat(llkStateTimeoutMs[llkStateD]) << "\n"
               << LLK_Z_TIMEOUT_MS_PROPERTY "=" << llkFormat(llkStateTimeoutMs[llkStateZ]) << "\n"
+#ifdef __PTRACE_ENABLED__
+              << LLK_STACK_TIMEOUT_MS_PROPERTY "=" << llkFormat(llkStateTimeoutMs[llkStateStack])
+              << "\n"
+#endif
               << LLK_CHECK_MS_PROPERTY "=" << llkFormat(llkCheckMs) << "\n"
+#ifdef __PTRACE_ENABLED__
+              << LLK_CHECK_STACK_PROPERTY "=" << llkFormat(llkCheckStackSymbols) << "\n"
+              << LLK_BLACKLIST_STACK_PROPERTY "=" << llkFormat(llkBlacklistStack) << "\n"
+#endif
               << LLK_BLACKLIST_PROCESS_PROPERTY "=" << llkFormat(llkBlacklistProcess) << "\n"
               << LLK_BLACKLIST_PARENT_PROPERTY "=" << llkFormat(llkBlacklistParent) << "\n"
               << LLK_BLACKLIST_UID_PROPERTY "=" << llkFormat(llkBlacklistUid);
@@ -892,9 +974,14 @@ milliseconds llkCheck(bool checkRunning) {
             if (pid == myPid) {
                 break;
             }
-            if (!llkIsMonitorState(state)) {
+#ifdef __PTRACE_ENABLED__
+            // if no stack monitoring, we can quickly exit here
+            if (!llkIsMonitorState(state) && llkCheckStackSymbols.empty()) {
                 continue;
             }
+#else
+            if (!llkIsMonitorState(state)) continue;
+#endif
             if ((tid == myTid) || llkSkipPid(tid)) {
                 continue;
             }
@@ -925,12 +1012,26 @@ milliseconds llkCheck(bool checkRunning) {
             // ABA mitigation watching last time schedule activity happened
             llkCheckSchedUpdate(procp, piddir);
 
-            // Can only fall through to here if registered D or Z state !!!
-            if (procp->count < llkStateTimeoutMs[(state == 'Z') ? llkStateZ : llkStateD]) {
-                LOG(VERBOSE) << state << ' ' << llkFormat(procp->count) << ' ' << ppid << "->"
-                             << pid << "->" << tid << ' ' << procp->getComm();
+#ifdef __PTRACE_ENABLED__
+            auto stuck = llkCheckStack(procp, piddir);
+            if (llkIsMonitorState(state)) {
+                if (procp->count >= llkStateTimeoutMs[(state == 'Z') ? llkStateZ : llkStateD]) {
+                    stuck = true;
+                } else if (procp->count != 0ms) {
+                    LOG(VERBOSE) << state << ' ' << llkFormat(procp->count) << ' ' << ppid << "->"
+                                 << pid << "->" << tid << ' ' << procp->getComm();
+                }
+            }
+            if (!stuck) continue;
+#else
+            if (procp->count >= llkStateTimeoutMs[(state == 'Z') ? llkStateZ : llkStateD]) {
+                if (procp->count != 0ms) {
+                    LOG(VERBOSE) << state << ' ' << llkFormat(procp->count) << ' ' << ppid << "->"
+                                 << pid << "->" << tid << ' ' << procp->getComm();
+                }
                 continue;
             }
+#endif
 
             // We have to kill it to determine difference between live lock
             // and persistent state blocked on a resource.  Is there something
@@ -969,12 +1070,13 @@ milliseconds llkCheck(bool checkRunning) {
                         // not working is we kill a process that likes to
                         // stay in 'D' state, instead of panicing the
                         // kernel (worse).
-                        LOG(WARNING) << "D " << llkFormat(procp->count) << ' ' << pid << "->" << tid
-                                     << ' ' << procp->getComm() << " [kill]";
+                    default:
+                        LOG(WARNING) << state << ' ' << llkFormat(procp->count) << ' ' << pid
+                                     << "->" << tid << ' ' << procp->getComm() << " [kill]";
                         if ((llkKillOneProcess(llkTidLookup(pid), procp) >= 0) ||
-                            (llkKillOneProcess(pid, 'D', tid) >= 0) ||
+                            (llkKillOneProcess(pid, state, tid) >= 0) ||
                             (llkKillOneProcess(procp, procp) >= 0) ||
-                            (llkKillOneProcess(tid, 'D', tid) >= 0)) {
+                            (llkKillOneProcess(tid, state, tid) >= 0)) {
                             continue;
                         }
                         break;
@@ -983,7 +1085,8 @@ milliseconds llkCheck(bool checkRunning) {
             // We are here because we have confirmed kernel live-lock
             LOG(ERROR) << state << ' ' << llkFormat(procp->count) << ' ' << ppid << "->" << pid
                        << "->" << tid << ' ' << procp->getComm() << " [panic]";
-            llkPanicKernel(true, tid, (state == 'Z') ? "zombie" : "driver");
+            llkPanicKernel(true, tid,
+                           (state == 'Z') ? "zombie" : (state == 'D') ? "driver" : "sleeping");
         }
         LOG(VERBOSE) << "+closedir()";
     }
@@ -1041,8 +1144,9 @@ unsigned llkCheckMilliseconds() {
 }
 
 bool llkInit(const char* threadname) {
+    auto debuggable = android::base::GetBoolProperty("ro.debuggable", false);
     llkLowRam = android::base::GetBoolProperty("ro.config.low_ram", false);
-    if (!LLK_ENABLE_DEFAULT && android::base::GetBoolProperty("ro.debuggable", false)) {
+    if (!LLK_ENABLE_DEFAULT && debuggable) {
         llkEnable = android::base::GetProperty(LLK_ENABLE_PROPERTY, "eng") == "eng";
         khtEnable = android::base::GetProperty(KHT_ENABLE_PROPERTY, "eng") == "eng";
     }
@@ -1069,8 +1173,21 @@ bool llkInit(const char* threadname) {
     llkValidate();  // validate llkTimeoutMs, llkCheckMs and llkCycle
     llkStateTimeoutMs[llkStateD] = GetUintProperty(LLK_D_TIMEOUT_MS_PROPERTY, llkTimeoutMs);
     llkStateTimeoutMs[llkStateZ] = GetUintProperty(LLK_Z_TIMEOUT_MS_PROPERTY, llkTimeoutMs);
+#ifdef __PTRACE_ENABLED__
+    llkStateTimeoutMs[llkStateStack] = GetUintProperty(LLK_STACK_TIMEOUT_MS_PROPERTY, llkTimeoutMs);
+#endif
     llkCheckMs = GetUintProperty(LLK_CHECK_MS_PROPERTY, llkCheckMs);
     llkValidate();  // validate all (effectively minus llkTimeoutMs)
+#ifdef __PTRACE_ENABLED__
+    if (debuggable) {
+        llkCheckStackSymbols = llkSplit(
+                android::base::GetProperty(LLK_CHECK_STACK_PROPERTY, LLK_CHECK_STACK_DEFAULT));
+    }
+    std::string defaultBlacklistStack(LLK_BLACKLIST_STACK_DEFAULT);
+    if (!debuggable) defaultBlacklistStack += ",logd,/system/bin/logd";
+    llkBlacklistStack = llkSplit(
+            android::base::GetProperty(LLK_BLACKLIST_STACK_PROPERTY, defaultBlacklistStack));
+#endif
     std::string defaultBlacklistProcess(
         std::to_string(kernelPid) + "," + std::to_string(initPid) + "," +
         std::to_string(kthreaddPid) + "," + std::to_string(::getpid()) + "," +
diff --git a/llkd/llkd-debuggable.rc b/llkd/llkd-debuggable.rc
new file mode 100644
index 000000000..724cb5ee0
--- /dev/null
+++ b/llkd/llkd-debuggable.rc
@@ -0,0 +1,19 @@
+on property:ro.debuggable=1
+    setprop llk.enable ${ro.llk.enable:-1}
+    setprop khungtask.enable ${ro.khungtask.enable:-1}
+
+on property:ro.llk.enable=eng
+    setprop llk.enable ${ro.debuggable:-0}
+
+on property:ro.khungtask.enable=eng
+    setprop khungtask.enable ${ro.debuggable:-0}
+
+service llkd-1 /system/bin/llkd
+    class late_start
+    disabled
+    user llkd
+    group llkd readproc
+    capabilities KILL IPC_LOCK SYS_PTRACE DAC_OVERRIDE
+    file /dev/kmsg w
+    file /proc/sysrq-trigger w
+    writepid /dev/cpuset/system-background/tasks
diff --git a/llkd/llkd.rc b/llkd/llkd.rc
index e538cdb91..b1f96a8f3 100644
--- a/llkd/llkd.rc
+++ b/llkd/llkd.rc
@@ -3,15 +3,8 @@ on property:ro.debuggable=*
     setprop llk.enable ${ro.llk.enable:-0}
     setprop khungtask.enable ${ro.khungtask.enable:-0}
 
-on property:ro.debuggable=1
-    setprop llk.enable ${ro.llk.enable:-1}
-    setprop khungtask.enable ${ro.khungtask.enable:-1}
-
-on property:ro.llk.enable=eng
-    setprop llk.enable ${ro.debuggable:-0}
-
-on property:ro.khungtask.enable=eng
-    setprop khungtask.enable ${ro.debuggable:-0}
+on property:ro.llk.enable=true
+    setprop llk.enable true
 
 on property:llk.enable=1
     setprop llk.enable true
@@ -19,6 +12,9 @@ on property:llk.enable=1
 on property:llk.enable=0
     setprop llk.enable false
 
+on property:ro.khungtask.enable=true
+    setprop khungtask.enable true
+
 on property:khungtask.enable=1
     setprop khungtask.enable true
 
@@ -36,9 +32,9 @@ on property:khungtask.enable=false
     write /proc/sys/kernel/hung_task_panic 0
 
 on property:llk.enable=true
-    start llkd
+    start llkd-${ro.debuggable:-0}
 
-service llkd /system/bin/llkd
+service llkd-0 /system/bin/llkd
     class late_start
     disabled
     user llkd
diff --git a/llkd/tests/llkd_test.cpp b/llkd/tests/llkd_test.cpp
index 3a15ff1e3..f54932bab 100644
--- a/llkd/tests/llkd_test.cpp
+++ b/llkd/tests/llkd_test.cpp
@@ -14,8 +14,10 @@
  * limitations under the License.
  */
 
+#include <fcntl.h>
 #include <signal.h>
 #include <stdint.h>
+#include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <unistd.h>
@@ -81,9 +83,12 @@ seconds llkdSleepPeriod(char state) {
         (GetUintProperty(LLK_CHECK_MS_PROPERTY,
                          LLK_TIMEOUT_MS_DEFAULT / LLK_CHECKS_PER_TIMEOUT_DEFAULT) !=
          duration_cast<milliseconds>(10s))) {
-        execute("stop llkd");
+        execute("stop llkd-0");
+        execute("stop llkd-1");
         rest();
         std::string setprop("setprop ");
+        execute((setprop + LLK_CHECK_STACK_PROPERTY + " SyS_openat").c_str());
+        rest();
         execute((setprop + LLK_ENABLE_WRITEABLE_PROPERTY + " false").c_str());
         rest();
         execute((setprop + LLK_TIMEOUT_MS_PROPERTY + " 120000").c_str());
@@ -92,8 +97,10 @@ seconds llkdSleepPeriod(char state) {
         rest();
         execute((setprop + LLK_CHECK_MS_PROPERTY + " 10000").c_str());
         rest();
-        execute((setprop + LLK_ENABLE_PROPERTY + " true").c_str());
-        rest();
+        if (!default_enable) {
+            execute((setprop + LLK_ENABLE_PROPERTY + " true").c_str());
+            rest();
+        }
         execute((setprop + LLK_ENABLE_WRITEABLE_PROPERTY + " true").c_str());
         rest();
     }
@@ -104,7 +111,7 @@ seconds llkdSleepPeriod(char state) {
     }
     default_enable = android::base::GetBoolProperty(LLK_ENABLE_PROPERTY, default_enable);
     if (default_enable) {
-        execute("start llkd");
+        execute("start llkd-1");
         rest();
         GTEST_LOG_INFO << "llkd enabled\n";
     } else {
@@ -123,8 +130,10 @@ seconds llkdSleepPeriod(char state) {
         llkTimeoutMs = LLK_TIMEOUT_MS_MINIMUM;
     }
     milliseconds llkCheckMs = llkTimeoutMs / LLK_CHECKS_PER_TIMEOUT_DEFAULT;
-    auto timeout = GetUintProperty(
-        (state == 'Z') ? LLK_Z_TIMEOUT_MS_PROPERTY : LLK_D_TIMEOUT_MS_PROPERTY, llkTimeoutMs);
+    auto timeout = GetUintProperty((state == 'Z') ? LLK_Z_TIMEOUT_MS_PROPERTY
+                                                  : (state == 'S') ? LLK_STACK_TIMEOUT_MS_PROPERTY
+                                                                   : LLK_D_TIMEOUT_MS_PROPERTY,
+                                   llkTimeoutMs);
     if (timeout < LLK_TIMEOUT_MS_MINIMUM) {
         timeout = LLK_TIMEOUT_MS_MINIMUM;
     }
@@ -285,3 +294,41 @@ TEST(llkd, driver) {
 
     waitForPid(child_pid);
 }
+
+TEST(llkd, sleep) {
+    if (checkKill("kernel_panic,sysrq,livelock,sleeping")) {
+        return;
+    }
+    if (!android::base::GetBoolProperty("ro.debuggable", false)) {
+        GTEST_LOG_WARNING << "Features not available on user builds\n";
+    }
+
+    const auto period = llkdSleepPeriod('S');
+
+    /* Create a Persistent SyS_openat for single-ended pipe */
+    static constexpr char stack_pipe_file[] = "/dev/stack_pipe_file";
+    unlink(stack_pipe_file);
+    auto pipe_ret = mknod(stack_pipe_file, S_IFIFO | 0666, 0);
+    ASSERT_LE(0, pipe_ret);
+
+    auto child_pid = fork();
+    ASSERT_LE(0, child_pid);
+    if (!child_pid) {
+        child_pid = fork();
+        ASSERT_LE(0, child_pid);
+        if (!child_pid) {
+            sleep(period.count());
+            auto fd = open(stack_pipe_file, O_RDONLY | O_CLOEXEC);
+            close(fd);
+            exit(0);
+        } else {
+            auto fd = open(stack_pipe_file, O_WRONLY | O_CLOEXEC);
+            close(fd);
+            exit(42);
+        }
+    }
+
+    waitForPid(child_pid);
+
+    unlink(stack_pipe_file);
+}